Electromechanical exchange system.



ma, AGRELL.

ELECTRGMECHAMCAL EXCHANGE SYSTEM.

APPLICATION'HLZD AUG-23,1907x 1,16%872, Patented Jan. 11, 1916.

I0 SHEETS-SHEET I.

j v-g ATTGR/VEY F. a. AGRELL. ELECTROMIECHANICAL' EXCHANGE SYSTEM. I APPLICATION FILED AUG-23, 1907.

g zg'yg Patented Jan. 11, 1916.

10 SHEETS-SHEET 2.

. MTORIIEY INVENTOR F. e. KGRELL.

ELECTROMECHANICAL EXCHANGE SYSTEM.

APPLICATION FILED AUG.23: 190T- Patented Jan. 11, 1916.

10 SHEETSSHEET 3.

INVENTOB v W $0M ATTOBNEX Wnusssss;

65? kid- 'F. G. AGRELL. ELECTROMECHANICAL EXCHANGE SYSTEM.

APLlCATION FILED AUG-23, 1907.

fi n E 1 NM P nnull nl nunub WITNESSES: @2r4 ATTORNEY F. G. AGRELL. ELECTROMECHANICAL EXCHANGE SYSTEM. APPLICATION FILED M643, 1907. 1,167,872. Patented Jan.11,'1916.

. 10 sums-sum 5.

F. e. AGRELL;

ELECTROMECHANICAL EXCHANGE SYSTEM. APPLICATION FILED AUG.23,1907.

1,167,872. Patented Jan. 11, 1916.

10 SHEETS-SHEET e.

o wmwm; 33W gm d w ammoz F. G. 'AGRELL. ELECTROMYECHANICAL EXCHANGE SYSTEM.

APPEICATION FILED AUG.23, 1907. I

Patented Jan. 11, 1916.

10 SHEETS-SHEET 7.

lm {W3 F. G; AGRELL.

ELECTROMECHANICAL EXCHANGE SYSTEM.

APPLICATQW FILED AUG,23,1907- 1.,167,872. Patented Jan. 11, 1916.

10 SHEETSSHEET 8.

. ajama/Q I I r QES @51 attomwgtin F. G. .AGRELL.

ELECTROMECHANICAL EXCHANGE SYSTEM. APPLICATION mm AUG.23, 1901:

1,167,872. Patented Ja11.11,1916.

l0 SHEETSSHEET 9.

lag/Wham M 31 Elnufluiioz F. G. AGRELL.

ELECTROMECHANICAL EXCHANGE SYSTEM.

' APPLlCATlON HLED'AUG.23,19.07.

1,167,872, Patented (12111.11, 1916.

I0 SHEETSSHEET 10.

Fig. 1a

Fig.1]. 1 159 1 5 142A 1% BEANS GUNN'AR AGBELL, OF STOCKHOLIK, SWEDEN.

ELECTROMECHAN ICAL EXCHANGE SYSTEM.

Specification of Letters Patent.

I Patented Jan. 11, 1916.

Application filed August 23, 1907. Serial No. 389,855.

To uZZ 1117mm it may concern:

Be it known that I, FRANs GUNNAR AounLL, a subject of the King of Sweden, and a resident of Stockholm, Sweden, have invented certain new and useful Improve ments in Electromechanical Exchange Sys tems, of which the following is a specification.

This invention relates to electro-mechanical exchange systems of that class which usually are called automatic exchange sys tems, in which connections are established between any two of a number of electrical circuits by the party desiring said connection without the assistance of another party (the operator). Systems of this class are sometimes employed for establishing the connections between several subscribers in a telephone system but may of course be used for establishing connections between any kinds of circuits. The systems heretofore de'ised can be divided into two different classes; one (which Fs now most in use) where every subscriber has a selective switch at the central station by means of which he can establish a connection with a number of other subscribers or selective switchesselectively. In this use the selective switches mustcomprise a switching de vice adapted to make connections between the line to which said selective switch belongs and a number of other circuits and selective means for directing the movement of the switch so as to make contact with the desired circuit. The other large :lass of automatic systems is characterized by the absence of selective switches individual to each circuit and their substitution by suitable means for connecting any circuit with a s itching circuit which then by means of a selector switch or a connecting device controlled by a selecting device completes the connection. A system of this last named class used the same principles as a manually operated system and is therefore similar to such a system to a certain degree. The switching circuits of the automatic system correspond to the cord circuits of the manually operated systems, the connecting device that connects at first the calling subscriber to said switching circuit and then the other end of said switching circuit with the subscriber to be called correspond to the plugs and jacks and the operators hands and the selecting device that registers the impulses sent bv the milling subscriber andutilizes them for directing the movement of the connecting device so as to make connection with the subscriber to be called corresponds to the brain and nerves of the operator. Such a system can, therefore, be devised in such a way that the utmost economy is used with regard to the expensive parts which necessarily are the selective means. This economy is obtained by utilizing the selective means for establishing connections for-a plurality of circuits in succession. The function of the connecting devices will now be purely automatic (not selective), that is, their action is. after having been started, independent of the will of the subscriber and is predetermined by the action of the selecting device.

The system which will be herein described belongs to the lastnamed class.

The object of the invention is to provide a system of devices and connections by means of which the principles set forth may be employed ith advantage in telephone exchanges having any desirable numher of subscribers. In systems of this class heretofore devised the number of subscribers that can be accommodated automatically has either been very much limited or, if a greater number of subscribers has to be accommodated, the principles set forth have not been thoroughly utilized. In addition to this the devices used for the establishing of the connections have been very complicated so that in spite of the obvious ad antages of such a system as compared with the first mentioned system that system is still almost exclusively in use.

In the accompanying drawings. Figures 1 and 2 are a diagram. showing the connections of an automatic exchange for one hundred subscribers using a known selective system. Figs. 3, i and 6 are d agrams which together show a system having one thousand subscribers: Fig. 5 shows a ditional connections which together with 1 s. 3. and 6 make up a system of ten thousand subscribers. Fig. 7 shows the cabling of the talking circuits of an exchange of one thousand subscribers. Figs. 8 and show the cabling of the talking circuits of an exchange'of ten thousand subscribers and Fig. 10 is an elevation of a release arrangement of the trunk connectors and Fig. 11 is a plan view seen from the top of said device.

The devices utilized in my system are subject to separate applications and will. therefore. be only briefly,described herein. some of these devices may also be substituted by old devices that fulfil the requirements of the system as the construction of all the devicesis to a certain degree non-essential for the operation of said system. 4

Before describing the system in detail I will briefly out-line its operation and that ofthe necessary devices so as to show the. relation of said devices to the systeii'i.

Brie description. of,,s'y .sz.(r1/z suitable number of subscribers for instance 100 are connected to the terininalsof a switching -dev ice which herein will be designated primary connector and which mayor may not be the same device as that wh ch later will be termed-the ten and unit connector.

The ofiice of the primary connector is to connect the calling subscriber to an incomin g switching circuit which at the time! is idle. The number of the switching circuits connected to said connector shall be so selected as to correspond to what is termed the maximum load of the exchange, that means. shall be equal or slightly h gher than the number of simultaneous calls that may be expected to'be the maximum among the.

subscribers of said primary connector. This maximum load is usually assumed to be less than ten per cent. of the number of subscribers but varies of course in different exchanges. .After the said connection is performed the switchingcircuit will connect itself to a selector which selector will receive i the nnpulses so asto connect that switching circuit either directly to the subscriber to y be called or. in the case of there being more subscribers in the exchange than can be. ac-

commodated by one connector. to a switchmg circuit that leads to the connector to which the desired subscriber is connectedQ Thisoperationbeing performed the selector disconnects itself so that it can be used for a number of subscribers use the same con- :calls. I The connection between the switching circ nts in the case of there being more than a hundred subscribers-is performed by sec/- nector. To prevent interference between simultaneously calling subscribers the connector must therefore be provided with a consecutive. arrangement which provides for a time interval between the action oflthe ondary connectors and the numbers of these "connectors depend upon the number of switching circuits, one secondary connector in the same locality.

may facilitate the connections between a hundred incoming and a hundred out-going switching circuits. The connection between the switching circuits is performed step for step. one step for can digit of the' subscriber's number so that. ii theexcl ange.for instance. has between one thousand and ten thousand subscribers. the connection is performed by means of two secondaryconuec tors. one thousand connector aiid one hundred connector. With only a hundred sub scribers in the exchange no secondary connector is needed. with thousand subscribers one secondary connector is used. An impor tant feature of my invention is now that by inserting a connector for each additional digit of the subscribers number any desired number of subscribers can be accommodated by the same cxchangi and another feature is that these connectors need not be placed It is therefore possible to divide a territory into a number of small subexchanges. let us say of one hundred subscribers each. and have the connections between the switching circuits per formed by a central or master exchange to which only the trunk lines from said sub-,

exchanges enter. These master exchanges may also be divided into group and the, CODIIGCUOUSbQt'WGBTI the switching circuits or trunks of. said master exchanges mayrbe performed at a. head exchange and tin.

method can be repeated as many times as may be desired so that all the subscribers of a. very large territory may be able to establishconnections with any other, subscriber. in said territory without the assistance of any operator. \Vith thismethod a very great saving in lines isalso accomplished 'as'the sub-excl'ianges may be established at avery short distance from the sub scribcrs stations and accordingly direct lines are only used for the shortest possible distances. all longer distances being covered by trunk lines to a number that may bi approximately valucd at ten per cent. of the number of subscribers. This idea is be lieved to be broz-idly new and opens new fields for the telephone on account of the. reduced cost.

The devices necessary for operating the. system arein addition to the.'subscribei"s iiistrunients and the relays,retardation coils,

generators. and batteries ordinaril used in a common battery exchangothe following: auton'iatically operated switching devices herein termed connia-tors .for making connections between subscribers lines and trunk lines and between trunk lines. senders at the subscribers instrun'icnts adapted to send theinipulses required for selection, selectors adapted to respond ,to'the action of the senders and direct'tho operationof the connectors.

c01mect0r.-SWitching devices adapttrunk col memes ed to be used in the automatic system are illustrated diagrammatically. It is not thought necessary to explain more than the most important features of the connectors in this specification.

The connectors used for connecting the subscribe s line to a trunk line, have three groups of connecting members so arranged that any member of one group can make contact 't i any member of another group. One of these last named groups is used for incom calls, other group for outgoing ca two groups are therefore connected trunk lines, the third group to an. .ibers lines. Arrangements are provided s of -hich the terminal of the callii is automatically (not selecti and ngen'ients may be provided to prevent member from being connecte'd trunk line which leads to a trunk connector which at the time is busy establish a connection. Consecutive arrangemer are provided so to prevent 1nterf ence between simultaneously calling s ll hen an outgoing call is to be served o er a trunk line this trunk line connects itself temporarily with the selector (:0 Ollll he operation of the connector.

select selects the terminal of the dei -auscs the same to make minals of said trunk done the selector is Olli said trunk line so that it any other trunk that therellestoring means common to connecting members, prefer- "h connecting device, is used the connecting members to the call is s also pro -ided s common restoring restoring any f the call.

ing connecdi; only slightly me before mentioned we groups of connecting n and the number of conem ers both groups is equal; 1 to the first connector group of the terniicond group of a preceding trunlr connector. The second group of the COilllB ction l l of terminals of the local connector s, its action is independent of the first of terminals. Said second group is L11 vided lllbG sections of which each section corresponds to a number in that git to which the trunk connector belongs. T e several terminals of each of said secticne are released by means of the action of third connected to an idle trunk line.

cctor is somewhatsimilar to the a selector selecting that special section andarrangements are provided by means of which the first idle terminal is automatically released. These means 'are common to the section.

The second group of terminals is connected to the second group of terminals of local connectors, each section to one con nector, or are connected to the first group of subsequent trunk connectors each section to a certain connector.

As in the local connector means common to the Whole connector are provided for restoring the terminals of one of the groups and might be used for the restoration of the second group. The main feature of the system utilizing these connectors is characterized by the independence of the talking circuits. A talking circuit when completed has no taps or multiple contacts or means that do not participate in the transmission of speech and the construction of the terminals is such that a very good connection is obtained between engaging terminals on accountof the comparatively great pressure between the contact surfaces during the connection. The trouble that so frequently arises in automatic telephone systems on account of intermittently broken circuits resulting from the loose contacts of present switching arrangements are thus Wholly eliminated. There are on the other hand no shunts of the talking circuit except that necessary for the current supply and as a result the transmission ability of a talking connection in thissystem is just as good as that of the best constructed and maintained manually operated cord circuits.

The select ice system.-As has been seen from the brief description of the automatic system set forth the action of the connectors must be directed to a certain extent by the action of selectors. Any suitable system of selectors and senders could be employed in conjunction With the connectors and,- as will be seen later, I have shown an automatic system using a step for step selecting system of known type in combination with the means set forth. as an example; For reasons that 'il fully stated hereinafter I pre- 0 a selecti e system difierent from s used up to this time. In this f any number in a digit is pera single impulse. I here will only state the main features of said system and t e selecto to able to slect any one of a contacts (preferably ten. correo the numbers in a. digit of l system of counting) Without using any source of current or complicated or expensive means at the sending stations, I employ several currents super mposed upon each other in circuits composed by the pulses are sent merely by making one or more simultaneous connections between the line wires or line wires and ground at said station.

Tim scZcctmL-Jn. my Patent No. 979,404 I have shown a device which operated by one or more of the superimposed currents mentioned will close the one or the other of a number of contacts. Any combination of selecting relays such as those employed for selective type write telegraph purposes could. of course, be used as a selecting device, but the device above referred to has great, advantage over present constructions inasmuchthat said device by means of cooperation between the selective relays causes a contact makerto make the desired contactdirectly so that the local circuit closed by said selector includes one contact only which of course eliminates a great many chances of trouble.

The senders-As sender for this selective system many widely diilerent devices could be used. The simplest would of course be to provide circuit closing keys at the subscribers station. each key making the connection that (:(n'responds to a certain number in a digit but asthiswould tend to make the operation of the automatic exchange too muchdependent upon the subscribeus use or misuse of the keys I have'designed aspecial type of sender that after having-been set to the number of the subscriber wanted before-calling, automatically makes the right connections necessary to select said subscriher in the right succession and without any assistance of the subscriber. This sender has been fully described in my Patent No. 927,469. A telephone system using such a senderis automatic in the broadest sense of the word as the sender as well as the exchan e a naratus after havin been started works perfectlyimlependentof the subscriber. its action being predetermined by the position to which the subscriber pres;

viously to giving the starting impulse has set the sender. The sender consists of two different comlnnations 0t switches, the first set which herein will be termed the.indicaexchange apparatus and for connecting and disconnecting the" telephone instrument to 'the line. It's-dependence upon the switchhook is limited to the starting impulse and the ending'impulse merely, the further 110-,

tion of the switch being dependent upon the exchange apparatus only by means of a detent pawl operated by an electro-magnet energized by the currents sent out from the tive arrangements are provided. Such arrangementshave been described in 'my Patent X0. 973.737 and it has not been thought necessary to describe these "arrangements in this specification or illustrate them in the drawings. it is only necessary to assume that in all cases where relays of electro-magnets would otherwise operate simultaneously the same by any of these arrangements are prevented from doing so. Referring now to Ifligs. 1 and 2 which drawings together form a diagram of connections of an automatic exchange having a number of subscribers small enough to be connected to one single connector in which case no secondary connector between the switching circuits is necessary, a subscribers station assumed to be calling is indicated at 1. As before mentioned I have in this example of an operative embodiment of my invention.employed the customary step for step selecting system and for that purpose a subscribers station is provided with a sending switch 2 which actuates a switch in the known manner so as to intermittently connect the one or the other side of the line to ground. I have assumed thatvthis switching mechanism when turned the first time grounds the one side of the line and turned a second time grounds the other side of the line a number of times correspmiding to the angle the disk is turned. The reversing arrangement for doing this has not been shown and can be of any suitable construction. The subscribers station is connected to the exchange by means of a circuit 3 and carries the insulatedly mounted terminals?) and (i. The arm is held in its inoperative position shown in the drawing liymeans of i a latch 10 which latch can be released by an electro-m'agnet 11 and engages the pin 12 upon the arm. \Vhen said arm is released it falls turning around the shaft 8.1 The lower end of therod 9 has a contact making spring 106 adapted to engage contact rods 49. The members of the second group of which only one =member.is*shown in the drawing as this .Wil *sutficeto explain the tro-magnet 19.

operation are indicated as arms 13 pivotally mounted at 11 and carrying an insulating block 15 which holds the terminals 16 and 17 connected to the incoming end of the switching circuit. These terminals are shown as rods which extend the whole way in front of the members of the first group so that any of these last named members can en gage the rods. The arm 13 is held in its inoperative position by means of the spring 18. In this position a falling member of the first group will go clear of the rods. The member can, however, be brought into a position where it can be engaged by said mem-' bers of the first group by means of an elec- When such a member is brought into said position the contacts 20 and 21 of a key 22 will be broken andthe contacts 23 and 24 of the same key be closed. As will be seen later the object of this key is to disconnect the terminals 16 and 17 from the switching circuit and connect the same to the selector. The switching circuit is indicated at 25 and 26 and ends at the terminals 27 and 28 of a member of the third group seen in Fig. 2. The arm-of said connecting member of the third group is marked 13 and is of the same construction as the member 13 with the exception that it carries a third terminal 29 the object of which will be described later.

At. Fig. 2 there is shown another member of the first group of terminals indicated by the arm 7 carrying the rod 9 locked by a latch 10 that can be released by the electromagnet 11. The arm is pirotally mounted upon the shaft 8 which is the same as that shown in Fig. 1 and the real position ot'said arm is, of course. above or below the arm 7 in Fig. 1. The terminals 5 and (3 are connected to the subscribers station 1 which of course is exactly similar to lin Fig. 1. The arm 13 engages a key 22 which operates in the same manner as the key 22, the objectof this key is to disconnect the terminal 27 and 28 and connect the same to a source of ringing' current when the arm is brought into its engaging position by means of the electro-magnet 30. The switching circuit and 26 is perfectly equivalent to a cord circuit of a manually operated switchboard,the

terminals carried by the member 13 correspond to theanswering plug and the terminals carried by the arm 13' correspond to the calling plug, the. key 22 corresponds to the operators listening key and the key 22 corresponds to the. ringing key. The system has been designed for common battery purpose and the cord circuit 25 and 26 has therefore been provided with means for supplying current to the subscribefis station for operating the transmitters of said station.' These means could be of any suitable kind but I have here shown the well-known arrangement of supplying the current through retardation coils and separating the direct current path of the called and calling circuit by means of condensers.

The means for restoring the terminals of the first group have in the diagram merely been indicated by an electromagnet 31. It is thought sutiicient to state that said electromagnet when operated causes a rod engaging the ends of the terminals to be restored to travel in a direction opposite that of the movement of said members.

The operation of the system is as follows: \Vhen subscriber 1 calls up he takes the telephone otithe hook, this causes current to go from the battery 32 over the line 33, electromagnet 11, lead 34, contact 35, lead 36 out on the one side 4 of the subscribers line from there through the induction coil 36, the now closed hook contacts 37, the trans mitter 38 and the normally closed contact 39. back to the line 3, lead 40, contact 41, lead 42 and the resistance 43 to ground and back to battery, energizing the electro-magnet 11 which releases the latch 10. The now free arm 7 will fall and the contact maker 106 will slide over the contact rods 49 until it comes to one which as that in the drawing is associated with an idle switching circuit. Now current will go from the battery over the lead 44, contact 45, lead 46, electro-magnet 30. lead 47, electroanagnet ll lead 48, contacts 49 and 106 to ground and back to battery. This causes the electro-magnets 19 and to swing the arms 13 and 13' into such a position that they can be reached by a falling member of the first group. Now the arms 13 and 13 and the contact rods 49 shall be so positioned that the arm 9 has passed the arm 13 when this is brought down to the engaging position so that it engages the member carried by the arm 13. \Vhen the arm 7 tell contacts and 41 are broken breaking away the current from the subscribers line so that magnet 11 will cease to operate. the latch thus going back to its position of rest. Now the springs 5 and 6 make contact with the rods 16 and 17 which rods by means of the key contacts 23 and 2% and the leads 50 and 51 are connected through the operating magnets 52 and 53 to the battery. The sender hereinafter referred to is similar to but not the same in construction as the one described in appli- -line 4 lead 54 and contact 58 to round.

The electro-magnet 53 will now operate the pawl 56 so as to raisethe selector shaft and rack 57 eight times. Now the subscriber operates switch 2 once to open and close the contact 58? when contact will be made be; tween ground and the line 3 once. Current then goes from battery over lead 55 electr0 magnet lead 50, contact 23, contacts 17 and (3 to the otherside 3 of the line and through contact 58 to ground, thus operating the pawl 59011 the magnet 52 so as to turn the shaft 57 one step which results in the sweepers (30 making contact with the terminals No. 81. \Vheii the shaft turns. .the normally broken contact between the springs til and (S2 is closcdallowing currei'it to gofrom batteryover spring til, springs (52. lead (33, the sluggish relay (5% and'lcad to' ground. This relay now closes slowly 'and closes at first the contacts 66 and (37.

When these contacts close current goes from the ground side. of the battery over the lead 65, contact on. lead (38. the lower spring of the sweeper (3d, the lower contact of the ter- I minals No. 81, lead (39, electro-magiiet 1 1 and lead 70 back to battery. Now this electro-magnet 11 operates to release the arm 7 of the selected subscriber.

released and the contact closed Current therefore goes from battcryqthrough lead 72. lead 73. common restoring relay 74. lead 75 contact (37. lead 76, upperspring of the sweeper .60. upper con- 71 accordingly tact of the terinii'ials number 81, lead 77.

contact'71 and resistance 43 to ground. The disconnecting relay 7+ is thus operated closingthe contacts 78, 79 and 80, contact 79 closes the primary circuit of a busy signal 81, through lead 82. self-breaker 87,

. primary winding 84. leadSa'i, contact 7!) and lead 86. so thatthe busy signal is started: the contact 80 closes the secondary circuit of said busy signal which then is connected through lead 83 to the line and the one side 3 of subscribei"s line and the other side through the lead. (57, contact 80 and lead 88 to lead 51 and the other side 4 of subscribers line. When disk 2 after the selecting operation goes backto its position of rest it closes the contact 39 thus connecting the subscrihe "s instrument to the line so that the subscriber is notified that'subscril'ier number 81 is busy by'ineans of the busy signal sound in his receiver a nd puts the same back on'the hook. \Vhen the contact 78 of the disconnecting relay 74 was closed current If this subscriber is busy however. said arm is'already The restorin' motor back to battery. The magnet 02 then opertact between springs tit and (-32 so that the current in the sluggish relay (it is broken and the same ceases to operate breaking away the current from releasing magnet 11' and the common disconnecting relay 7% which both cease to operate.

in the restoring motor 31 which goes back to its position of rest. hen, however, the restoring motor restored the member 7 to its bosition of 'rest contact "was broken between the rod ti and the contact Hit). The current 'in the electro-niaguets 19 and 80 is thus broken away and the arms '13 and 13 go back to their positions of rest breaking away the selector 'l'rom the switching circuit. lirenrthing is-now restored to the respec tire rest positions. It. however. the line No. S1 should happen to be idlethe arm f would have been in its rcst position and the contact 71 broken. \\'hcu the selector therei'ore had'selcctcd the tci'iiiiiials No. 81 no currentcould have gone over the disconnecting relay T-l so that no busysignal would have been given. The magnet 11 would then have released the arm 7 which falls and allows the terminals 5. (i and 97 to make contact with the rods 27. 29 and 29 respectively. When this contact is rt'ormed current will go "from the ringing generator 96 over the lead 7. contact lead l con- 1 tacts .27 and 'to the one side t of the sub'-.

scribens line amt from there bell-and the condenser back through the other side ol the line. contacts 3' and and lead 100, and contact till. lead hi2. contact lt i'ot-theilisconiiccting relay ltlt and lead 105 back to the generator. thus signah iug the subscriber. When contact is formed through the betu'eenhthe contacts 05 and 29 current {Ices from the battery over lead 107, relay 10S, lead 10 contacts 3 and 9;) to ground and back to battcip'. ltclay IUS is thus operated breaking the contact L which breaks away the current from electroanagnets 3t and 19 causing the arms 13; and 13 to go back to their positions of rest. the return ol arm 13 tai'dation coil'dll. l ad .1 l! to the one sitit it; of the calling subscribcns half of the switching cii'i'u it and back l'roni tlie.line of said ball through lead ill) supervisory relay 115 and lead l to to the groundside-ot the batte"r and to the lled subscriber I hen relay 7t ceases to operate the busy signal is disconnected and the currentbroken through lead 110, retardation coil 117, lead 118, to the one side 26 of the called subscriber's half of the switching circuit and back from the other side 25 through lead 119, supervisory relay 120 and lead 116. As soon as the switching circuit'is connected for conYcrsation the relay will be energized as the calling subscriber has his receiver of? the hook and the contact 121 on said relay is thus broken. As soon as the called subscriber takes the receiver ott the hook at the station 1 the relay will'also become energized and the contact 122 on said relay will be broken. As soon as the sluggish relay 10S operates the contact 123 on said re lay is closed connecting the disconnecting relay 1% to battery at the one side. The other side is open at the contact 121 and will re main so until both subscribers have put their telephones on the respective hooks when relays 115 and 120 cease to operate closing the contacts 121 and 122. current will then go from battery over lad 44. contact 123, lead 124. relay lfll and lead 125. contact 121.. contact 122 and leads 126 and 11b to ground and back to battery. The disconnecting relay thus operates, breaks the contact 103 and closes the contacts 127. 129 and 12! (urrent will then go from battery over lead 130 contact 12?. lead 413. electro-magnet 30, lead 47. clectro-magnet 1 lead 133 contact 128 and lead 132 to ground and back to batterv energizing the clectro-n1agnets 19 and 30. The arms 13 and 113 will thus be swung in so as to allow the terminals or arms 7 and l" to be discomuated. 'lhe signaling -circuit of the generator 96 is broken at the contact 103 so that the called subscriber does not receive any new signal. ll'hen contact 129 closed current also went from batterv over lead 72. restoring motor 31, lead 153 contact 12 and lead 132 to ground so that the said motor operates so as to restore the terminals carried by arms 7 and T to their original position of rest. To avoid duplication ot the drawing the motors 31 of Figs. 1 and 2 maube. considered as operated by either the ailing or called subscriber. as the connections are. the samef During this restoring operation the contact will be broken between contacts 2 and 5 thus breaking awav the current in relay 109 wh ch slowlv goes back to its posi tion of rest breaking the contact 123 and closing the. contact again. When contact 123 is broken the relay llll ceases to onerate breaking its contacts 127. 128 and 129 and closing the contact 103. The current is thus cut awa from the restoring motor 31 and the clcctro-magnets l and 30 so that the said moto' and th arms 13 and 13' go back to their positions of rest and when the term nals oi the arms 7 and 7 reach their original positions the contacts o erated in the same connect the respcctiveilines to the releasing magnets 11 and 11' and the resistances 43 and 43. Everything is now restored to the initial rest positions.

As before mentioned, means are provided to prevent simultaneous operation of the terminals of several subscribers and means may be adapted when operated to prevent disconnecting a pair of subscribers ha ing finished their conversation until the device is idle.

In Fig. 7 I have shown a very convention aliZed diagram of the connectors the tall ting circuits l ading to and from the some for an exchange up to one thousand subscribers. For such an ex hange 1 eninloy only one trunk connector represented c diagram at A. Said trunk connector i adapted to make. the connections between all the switching circuits of ten local nectors designated by B. Each local con nector is adapted to connect 100 subscribers lines which lines 1 have shown in ten t pair cables shown at the upper end of the figure. Each connector has ten incoming switching circuits shown at C as a ten-pair cable. These incoming switching circuits are connected to the terminals of the first.

group of the trunk connector A, wt", group is indicated in the drawing by upper half D of the circle. Each local connector has also ten outgoing switching circuits a connected to the second group of terminals of the trunk connector A indicated at F. g

The way of connecting a subscriber with another will be easily understood from th' diagram. rlup iosing a siibscrihcr of the connector l3 calls up his line will then get connected with the first idle switching circult of the cable which switching circuit in the manner described in connection with Figs. 1 and 2 connects itself to the selector of said trunk connector. The subscriber will now select the hundred to which the desired subscriber belongs and when this selection is done the connector will automatically make connection between the cal switching circuit oi the ten that lead to the local connector having said hundred numbeix which we may assume to be 1 Connccticn is thus formed betweei a switching circuit of the cable and a switching circuit ot' the cable ll. iiow this switching circuit connects itselt' with the selector of the connector B" and when the subscriber has selected the desired ten and unit the cor responding connecting member which we may assume to be connected to a line of the cable (l is released and makes contact with the switching circuit. Thus the complete talking circuit is formed.

The same principles used in the cinbodiment of mv invention as now described for a small exchange may be applied to an ex change having any number of subscribers.

' carrying out my invention for a large numher of subscribers, one of these principles is that the lccal connector not only connects the suhscribefs line to an idle switching circuit but'tosuch an idle switching circuit which leads to a trunk connector which at the time is idle. This results in. a greater speed of operation and on the other hand makes it possible to.put one or more ofsaid trunk connectors with associated means out of'comnnssion without disturbing the operation of the exchange.

In Figs. 8 and 9 I have shown the cabling of the talking circuits as the same would be in an exchange having up to ten thousand subscribers (fourth power-of ten). Such an exchange would have one hundred local connectors andten primary and ten secondary connectors, but for the sake of clearness I have in Fig. 8 abridged the number of local connectors to sixteen (the square of 4) and accordingly shown only four primary and four secondary trunk connectors. In Fig. 9 however, which represents the connections between the primary andthe secondary connectors I- have shown twenty trunk connectors but only connected a few of these completely in order to prevent confusion of the drawing; In said Fig. 8, B represents as before the local connectors, (3 their incomingswitching circuits and I) the outgoing'switching circuits. H represents the primary connectors and .I the sec ondary connectors. The function of the primary'connector is to connect the incoming switching circuit with an switching circuit that leads to the selected hundred or secondary connector which function is to connect this intermediate switching circuit \vithan out going switching circuit leading to the local connector to which.

The local "sandbut lowei .than one hundred thousand,

the desired subscriber is connected. connectors. have. as the corresponding connectors in Fig. 7, ten incoming and tcln outgoing switching circuits and are adapted to take. hundredsubscribers.lines. All the ten outgoing switching circuits E are 0on ncctcd to the. same secondary connector J but the incoming switching circuits are for the reason stated above connected todillercnt primary trunk connmctors II. In Fig.

8 I have shown the incoming switching cir-' cults of each local connector distributed over the total number of primary trunk conintermediate nectors. This insures, of course, the best distributions of the calls. but this distribution may b carried out in a manner insuring good results for all practical purposes by distributing the incoming switching circuits among smaller number ot' primary connectors. In Fig. 9 I have shown the cabling of the intermediate switching circuits. The same 'is easily understood by a glance at the figure and it is not thought necessary to explain further than to state that from each primary connector l'I- g'ocs ten switching circuits reprcsented'as a ten- .pair cable K to each secondary connector J. The forming of the talking connection between two subscribers is now easily understood from these diagrams. subscriber connected to the local connector B calls up. His connecting member will thenmake connections with the. lirst not busy switchingcircuit C that leads to an idle primary connector II. Supposing II Supposing a is busy. the. line t will be inaccessible for the subscribers terminals which instead will connect with the first idle line which may he assumed to be C" which leads to the connector H. The switching circuit as before described connects itself to the selector oi" said primary trunk connector II and theconnects the internualiatc switchingcircuit.

of cable]? tothe first not busy out-going switching circuit otthc cable It whereupon the. local conncctor ll connects the switching circuit with the. selected subscriber in the ma nncr'bcforc named.

We will as-' It is how easily seen'how a'connection between ahy two subscribers ol' a telephone system of any number is to be built up. For a number ol'\subscr|la-. rs exceeding tcn tho||- it will. of course be necessary to introduce another trunk connectormaking'conncctions lzetwcen two intcrmmliatc switching circuits. .,\s will be seen from tlicqliagrains I). i. 5 and'ti which willbe explainedlater, all the functions ol the switching circuits may be performed through three conductors only of which two serve. alternatively as the talli ing circuit and for operating tl and tho thlrd cmuluct q'r'tiis c) facilitating the op pl the connectors. a lo connectors.

It is thus easily seen that the diiierent connectors need not to be,installed in the same exchange but can be installed 'in different exchanges so that, foi instance, each local connector with associated means may form a sub-exchange, each primary trunk connector may form a central exchange for ten such local connectors, each primary and each secondary trunk connector will form a trunking exchange and if a number of subscribers larger than ten thousand is involved the intermediate trunk connectors may constitute a master exchange. lVhen my invention iscarried out in this manner it will not be practical to distribute the incoming trunks over all the primary trunk connectors of the system as has been shown in Fig. 8 but good results can be obtained by dis tributing said switching circuits over a couple of primary connectors only. That the employment of the now mentioned suband master-exchange principle results in a great saving of lines and conduit is evident.

Before describing the diagrams Figs. 3, 4, 5 and 6 it will be necessary to describe a little detail of the arrangement of the trunk This detail is a device for releasing the first not busy terminal of a selected group and is shown in Figs. 10 and 11 of which 10 is a side elevation of the device partially in section and Fig. 11 a top plan view of'the same also partially in section. In these figures 135 represents arms upon which a rod 136 carrying the terminals of the second group of the trunk connectors are mounted. These terminals are not shown in the drawing. The arms are pivot ally mounted upon a shaft 137 and are adapted when released to fall in the direction of the arrow in Fig. 10. when the terminals make connection with the terminals of the first group. In Figs. 10 and 11 ten such arms are shown representing the terminals of one section of said group, that is, the section that is selected when the selector takes a position corresponding to a certain number. The arms are held in their normal position of rest by means of a latch 138 of peculiar shape engaging a member 139 common to all the connecting members. Each latch is provided with a projection 140 adapted to be engaged by a member 141 which is provided with successively rising projections 142. This member is slidably mounted upon an armature 143 of an electro-magnet 144 and extends by means of the spring 145 to move toward the connecting member. When all the members are in their initial positions only the uppermost projec tion 142 of said member 141 is in engagement with a latch, that is, latch 138 The armature 143 is pivoted at 146 so that when it is attracted by the electro-magnet 144 it will raise the member 141 which thus will release the latch 13S so that the member 135 will be released. The member 141 will during this operation slide out until the next projection 142 of the same rests against the edge of the projection 140 and when the current ceases to flow in the electro-magnet the armature and the thereto connected member 141 will descend to their lower position of rest where the member 141 will engage the latch 138 in the same manner as it before engaged 138'. The next time the electro-magn'et is energized the member 135 will thus release and so on. If now a released terminal such as 135 is restored again the edge 147 of its latch will push back the member 141 so that this member will be the next to be released and so on. Thus it is seen that when the selector puts current out on the electro-magnet belonging to the selected section, the first, not

busy connecting member will always be released.

In the diagram Figs. 4, 5 and 6 which together form a diagram of a connectionbto be established between a calling anda called subscriber in a system. having up to ten thousand subscribers, Fig. 3 shows the calling station and that part of the local con nector which is used to connect the calling line with an incoming switching circuit. Fig. 4 shows that part of the primary trunk connector with associated means which is employed in establishing the connection between said incoming switching circuit and the selected intermediate switching circuit. Fig. 5 shows that part of the secondary trunk connector with the associated means which is employed for establishing the connection between said intermediate switching circuit and an outgoing switching circuit and Fig. 6 shows that part of the local connector with associated means which is employed for establishing the connection between said outgoing switching circuit and the selected subscribers line and shows only the called subscribers station to such an extent that is necessary for understandingthe operation of said station when called. Omitting the diagram Fig. 5 the three remaining sheets form a diagram of a connection between two subscribers in a system having up to one thousand subscribers and adding one sheet of drawings exactly the same as Fig. 5 between Figs. 4 and 5 or 5 and 6 would give the complete diagram of a connection between two subscribers of a system having up to one hundred thousand subscribers. If the connecting devices are not placed in the same exchange, the same diagrams also represent sub-exchanges and central exchanges so that, for instance, Fig. 3 plus Fig. 6 make up the diagram of a subexchange and Figs. 4 and 5 make up the cen tral exchange. The added sheet would in sucha case be a diagram of the master exchanges. Notwithstanding the difierent ways in which the diagrams thus can be read together, it has been thought necessary only phone) at 149. The instrument is equipped with an automatic sender 150 the function of which is to send the impulses necessary for operating the selector at the central station in right succession and an indicator switch 151 for predetermining the impulses to be sent. The impulses as I have before men'- tioned are sent by making different connec' tions between the two line wires 152 and 153 and ground. The in'ipulses are the following: 1:Line wire 152 through condenser and resistance to ground; line wire 153 through condenser and resistance to ground. 2 :Line wire 152 through condenser and resistance to ground. 3:-Line' wire 153 through condenser and resistance to line wire 152. =1:Line wire 153 through condenser and resistance to ground. 5: Line wire 152 through resistance to line wire 153 and same linewire through condenser to ground. 5: Line wire 153 through resistance to ground and line wire 152 through condenser to ground. 7 :Line win 152 through resistance to ground. 8 :Line wire 153 through resistance to line wire 152. 9 Line wire 153 through resistance to ground. 10 :Line wire 152 through resistance to ground and line wire 153 through condenser to ground. These circuits can be traced from the contacts of the indicator switch 151. The resistance mentioned is the electro-magnet 1545 whose function will be described later. The switch 151'fhas as many sets of brushes 155 as there are digits in the number tobe selected although I have in order to prevent confusion of the, drawing shown only one set in Fig.- 3'. These sets of brushes are so arranged that they can take any of the positions possible, simultaneously. These brushes lead to contact plates 156 of the sender switch 15.0. There are three rows of such contact plates left unconnected in the drawing and these are adapted to be connected with the three other sets of brushes.

155 which arenot shown in the drawing. On the segments 156, contacts 157, 158 and 150 are adapted to ride. These contacts are connected to the line and to the ground and are in the drawings shown mounted upon a slidable toothed member 160 connected to the switch hook 161 When the telephone is on the hook the'switch takes the lower position shown in the drawing but when the telephone is taken off the switch is raised by means of the spring 162 until it is arrested by the detent pawl 163 operated by the armature 161 of the electro-magnet 151. hen this happens the receiver induction coil isconnectedto the line and the electro- U directelectrical connection with the rod.

The line is normally supplied with current from the battery 32 over the bus-bar 166, lead 171, right side winding of relay 1.68, lead 170, contact 35 to the 'oneside 153 of said line and through bus-bar 165, lead 167, left side winding of the relay 168, lead 169, and contact 4:1 to the other side 152 of the line so that when the subscriber at station 148 takes the telephone off the hook the switch will rise one step and then as current will go through the magnet 151 the pawl 163 will engage the rack 160 with its lower end. It is evident that when the current is broken at the exchange the pawl 163 will release the rack 160 one step so that the brushes 157, 158 and" 159 will advance to their third position.

The members 7 of which I have assumed one hundred to be assembled 1n one connec' tor, are held in their initial position of rest net, for instance, supposing the last two digits of the calling subscribers number are 2 and 3, then the member 7 would be released by the co'ciperatlon of the ten magnet No. 2 and the unit magnet No. 3. This 11'.

cotiperation principle is made use of in my,

Patents Nos. 1,061,650 and 1,061,651.

When. the subscriber 118 calls up as before said, the switch will take its secont position and current will go from batte y' 32, bus bar 166, lead 171, line relay 168,,l'ead 170, contact 35*, the one side 153 of th "subscribers line brush 159', correspondin contact 156, lead 301, the transmitter, the induction coil 302, lead 305, to the contact 156 corresponding to brush 157 and, back th igh the other side 152 of the 11118, contact 11, lead 169, right hand winding of relay 168, lead 167 and bus bar to the other side of the battery. Thus relay 168 is 

